Keyboards are known to the present inventor in which the keys, when operated singly, carry out respective functions and, when two or more are operated together substantially simultaneously, carry out a further function, which is called “chordal operation”. This is different from simply playing two keys together on e.g. a piano, which simply carries out the functions of both but does not carry out any new and different function.
Prior art keyboards with large numbers of keys are generally not economical in layout or, if they are, are not conducive to easy learning of the key functions and the chordal possibilities. Other disadvantages are discussed below.